1. Field of the Invention
The present invention relates to a dimming driving system and a dimming controller, and particularly to a dimming driving system and a dimming controller that can accept a plurality of dimming signals.
2. Description of the Prior Art
A light-emitting diode driving circuit with a dimming function needs to have at least three possible dimming manners: a phase truncation (TRIAC) dimming, a pulse-width modulation (PWM) dimming, and an analog level dimming. However, control chips provided by the prior art only can provide one or two of the at least three possible dimming manners.
FIG. 1 is a diagram illustrating a light-emitting diode driving circuit according to the prior art, where the light-emitting diode driving circuit has a flyback topology, a transformer of the light-emitting diode driving circuit has a primary winding PRM, a secondary winding SEC, and a auxiliary winding AUX inductively coupled to each other. As shown in FIG. 1, the transformer roughly separates a primary side circuit from a secondary side circuit, so the primary side circuit and the secondary side circuit are inductively or capacitively coupled to each other, and have a primary side ground wire 22 and a secondary side ground wire 24, respectively. A power factor correction (PFC) controller 26 can control a power switch 34 to turn on/turn off to make the transformer store power/release power. When the transformer releases power, the secondary winding SEC builds an output voltage VDD on an output power line VDD through a rectifier diode.
A series of light-emitting diodes 28 are coupled between the output power line VDD and the secondary side ground wire 24. An operational amplifier 30 can provide a constant voltage feedback mechanism through a photo coupler 36, so an operational voltage VDD does not roughly exceed a value corresponding to a constant voltage reference voltage VREF-CV when the plurality of light-emitting diodes 28 are turned off. An operational amplifier 32 and a current detection resistor RS can provide a constant current feedback mechanism through the photo coupler 36, so the constant current feedback mechanism can make current flowing through the series of light-emitting diodes 28 be roughly equal to a constant current reference voltage VREF-CC dividing by a resistance of the current detection resistor RS when the series of light-emitting diode 28 are turned on.
However, the phase truncation (TRIAC) dimming utilizes a primary side of the light-emitting diode driving circuit to dim the series of light-emitting diodes 28. For example, a voltage divider can make the PFC controller 26 detect an input voltage VIN on an input power line IN. Therefore, the PFC controller 26 can control the current flowing through the series of light-emitting diode 28 at a secondary side of the light-emitting diode driving circuit according to a period ratio of the input voltage VIN being about 0V to the input voltage VIN exceeding 0V. But, control accuracy of the current flowing through the series of light-emitting diode 28 provided by the phase truncation (TRIAC) dimming is not enough, and the phase truncation (TRIAC) dimming can also not provide functions of pulse-width modulation dimming and analog level dimming.